Feeble human eyes require a certain level of light to see color. Cameras, though, have the magical ability to expose the world at night. Husband-and-wife photographers Diane Cook and Len Jenshel have been playing with long-exposure photography for years — more specifically, in moonlit gardens.

National Geographic magazine hired the couple to shoot a series specifically for the March issue. Even more photos, including a few from their personal archives, are on display at the magazine's headquarters in Washington, D.C.

The stars have to align for one of these photos to turn out — almost literally. "Moonlight has its own soft, romantic poetry," the couple writes in a National Geographicdispatch, "but to get it right when photographing a garden at night requires some hard science."

The moon's orbit wobbles, for one, so it might never crest above tree line. There's also the unpredictability of weather. And for this specific magazine series, the photographers sought out specific flora — some of which only blossom once a year. The odds of successfully capturing this blooming waterlily were not high.

But that careful, meditative process is part of the pleasure. On National Geographic's website, Cook and Jenshel reflect about the making of one photograph in particular — a 40-foot cherry blossom tree in Kyoto, Japan. "Standing there is like going to a mountaintop in Tibet or India and finding this elder who's going to grant you wisdom," Cook says.

It was a bittersweet moment for Cook, whose father had just died.

"We fully understood then what the Japanese had been practicing for centuries," she says. "That in our busy lives we need to make time to appreciate life's ephemeral nature."